In many integrated circuit fabrication processes, it can be difficult to maintain uniform conditions. As a result, integrated circuits can have different electrical characteristics. For integrated circuits that vary outside of a desired range of an electrical specification, the integrated circuits must be discarded or modified to meet the electrical specification. Accordingly, it can be beneficial if the integrated circuit contains a trimming circuit to adjust the electrical characteristics of the integrated circuit.
In some integrated circuits, including read only memory (ROM) based devices, it can be difficult to store trimming related information because writing the trimming information into memory would use valuable memory. Other techniques of storing trimming related information that don't have memory have their own limitations. For example, floating gate cells are reliable but are expensive to make. Laser fuses can be used, but these fuses can be difficult to manufacture and test. Electrical fuses may also be used, but the state of an electrical fuse can be difficult to determine if the fuse is only partially blown. Accordingly, there is a need for a memory cell able to reliably store trimming related information, and that can be manufactured relatively inexpensively.